The present invention relates to a composite wood board product and its method of manufacture. More specifically, the present invention relates to an improved method of manufacture and an improved product created using a hog fuel mat with a catalyst. The method and resulting product rely on adhesives naturally present in the hog fuel that are dispersed throughout the board product during formation.
Hog fuel is generally sawmill refuse that has been fed through a disintegrator or hog by which the various sizes and forms are reduced to a practically uniform size of chips or shreds. Hog fuels generally contain approximately 70% to 95% bark with the residue being primarily wood.
Bark boards made without synthetic resins are known. In an Article entitled xe2x80x9cBark Boards Without Synthetic Resinsxe2x80x9d published by S. Chow in Volume 25, No. 11, of the Forest Products Journal, pages 32 to 37, dated November, 1975, is disclosed making bark boards without the addition of synthetic resin by forming bark pieces into a mat and then compressing the mat in a platen press at a predetermined pressure and temperature. During the pressing step a vacuum is applied continuously to the platens to withdraw steam and water vapour. The boards were tested for dry bending strength and compared with particle board. Favourable results were obtained, however, the product has never achieved success in the marketplace.
Commonly owned U.S. Pat. No. 5,725,818 entitled MANUFACTURE OF A HOG FUEL BOARD and U.S. Pat. No. 6,120,914 entitled HOG FUEL BOARD, the disclosures of which are incorporated herein by reference, disclose a method of manufacturing a hog-fuel board and a hog fuel board product, respectively. The above patents are based on the idea that using hog fuel rather than carefully selected bark results in at least a small percentage of wood being automatically included with the bark, and a percentage of wood over 5% adds additional strength to a bark board product. Inasmuch as hog fuel already has wood particles therein, it is not necessary to separate the wood particles from the bark. Hog fuel is ideal as it comes from the hogging process that involves removal of bark from raw logs. Furthermore, the above patents disclose that it is possible to produce a hog fuel board without having to apply a vacuum to a platen press as required by Chow. The vacuum step is an expensive operation which may well have prevented the bark boards disclosed by Chow from being commercially feasible. The manufacturing process disclosed does require modification of existing platen press equipment to operate at a higher platen temperature.
After further development work, it has been discovered that the addition of a catalyst, ammonium chloride, in relatively small amounts to the hog fuel results in a board having improved strength that can be formed at lower platen temperatures. It is important that the catalyst be added uniformly throughout the hog fuel. This development only increases the commercial feasibility of the hog fuel board product.
The hog fuel board of the present invention is manufactured in platen press equipment operating at platen temperatures that are generally 10xc2x0 C. to 40xc2x0 C. lower (in the range between 230xc2x0 C. to 290xc2x0 C.) than in applicant""s previous manufacturing method. The internal bond strength of the boards manufactured using the ammonium chloride catalyst is also significantly increased such that the boards have a strength greater than particle board without requiring the use of added adhesives. Boards made of hog fuel have greater strength in bending than boards made of bark alone. Furthermore, hog fuel boards have excellent dimensional stability for all uses as compared to other wood composite board products.
In one embodiment, the present invention provides a hog fuel veneer board comprising: a compressed hog fuel mat containing about 80% bark by weight and about 3% ammonium chloride by weight, the remainder being primarily wood residues sandwiched between veneer sheets, the board having adhesives naturally present in the hog fuel to maintain board cohesion, the adhesives dispersed throughout the mat from heat and pressure applied to form the board. The veneer sheets provide smooth woodgrain exterior surfaces suitable for furniture and many other uses.
The present invention also provides a method of forming a hog fuel board comprising the steps of: forming a hog fuel mat containing between about 70% and 95% bark by weight and between about 1% to 7% ammonium chloride by weight uniformly distributed through the hog fuel mat, the remainder being primarily wood residues, with flexible non-sticking layers on outside surfaces, between screens in a preheated platen press and pressing the mat in the platen press to preset stops for a predetermined time and at a predetermined pressure to cause adhesives naturally present in the hog fuel to disperse throughout the board.
In another embodiment, a lumber product has a hog fuel coating thereon comprising:
a compressed hog fuel mat coating containing about 80% bark by weight and about 3% ammonium chloride by weight, the remainder being primarily wood residues, the mat coating held together and held to the lumber product by adhesives naturally present in the hog fuel, to maintain cohesion in the mat and to the lumber product, the adhesives dispersed throughout the mat from heat and pressure applied to apply the coating to the lumber product. The finished product has the natural protection that bark gives to a tree, and provides improved chemical resistance, fire resistance and decay resistance over standard untreated lumber products.